Most businesses that sell on Trendyol and also run their own online store hit the same problem sooner or later: stock is kept in two places, one gets updated and the other doesn’t, and the last unit sells on both channels at once. The fix is to connect Trendyol to your site through its API.
Using a ready-made integrator is also an option. Either way, knowing how things work under the hood helps you ask the right questions.
Where to find your API credentials
In the Trendyol seller panel, click your store name at the top right and go to Hesap Bilgilerim > Entegrasyon Bilgileri (Account Info > Integration Info). You’ll find three values there: Seller ID, API Key and API Secret. Only the main (admin) user can see this section, so if a colleague you added later says the menu isn’t there, that’s why.
These credentials are the keys to your store. Don’t pass them around by email and don’t hard-code them. When you stop working with an agency, rotate them.
Authentication and the first error
Requests use Basic Auth: API Key and Secret joined and base64-encoded. Nothing unusual there. What trips most people up on the first try is the User-Agent header. Trendyol requires it in a specific format: your seller ID, then the name of whoever built the integration. If you wrote it yourself, something like “1234 – SelfIntegration”. Requests without it come back with a 403, and the error message doesn’t make the reason obvious.
Test environment
Trendyol has a separate stage environment, and its credentials are completely different from production. To reach it, your server’s IP has to be authorized by Trendyol, which you request through seller support. If stage returns 503, your IP probably isn’t authorized yet.
This can take a few days, so start it at the very beginning of the project. On stage you can create test orders and run the order flow end to end, which is much safer than trial and error on your live store.
Product upload: where the real work is
Sending a product to Trendyol is a single request on paper. In practice, category and attribute mapping takes most of the time.
Every product belongs to a leaf category, and each category has its own required attributes such as color, size, material or gender. Their values usually aren’t free text but have to be picked from Trendyol’s list. The “Navy” on your site needs its Trendyol equivalent. Brands are matched against Trendyol’s brand list the same way.
Also, product create and update requests don’t return a result right away. You get a batch request ID and check separately whether the products were accepted. Integrations that skip this check think the products went through and miss rejected ones for weeks.
Our advice: fetch the category tree and attribute lists once and store them, check required fields on your side before sending, and put rejected products in a list that someone actually looks at.
Stock and price updates
Stock and price are updated by barcode, so barcodes must match exactly between your site and Trendyol. Using the same barcode on two variants is the most common cause of stock mix-ups.
A few rules worth knowing:
- You can send at most 1,000 items per request.
- Sending a request with identical content again within 15 minutes returns an error. Send only what changed instead of the whole catalog every time.
- The number of price updates per barcode per minute is limited.
Leaving stock sync to a scheduled job alone is risky. When an order comes in on your site, Trendyol stock should drop right away, and vice versa. On best sellers, holding back the last one or two units as a buffer greatly reduces overselling.
Orders
Orders come from Trendyol as shipment packages. You can poll for them at intervals or register a webhook so Trendyol notifies you. Webhooks are faster, but it’s a good habit to also run a periodic check that compares order lists in case a notification goes missing.
The order flow also includes updating package status, sending the invoice link to Trendyol and shipping details. Connecting your e-invoice provider is a separate job; we cover it in our e-invoice and e-archive guide.
Rate limits
The Trendyol API has rate limits and returns 429 when you exceed them. Since September 2026, limits are set per service group and scale with your store’s listing limit. The most common mistake we see is not logging those 429s: the integration silently misses orders and nobody notices. Log the result of every request, and on a rate-limit error wait and retry.
Ready-made integrator or custom integration?
If you have few products, a simple category structure and your platform already has a Trendyol connection, setting that up properly is often enough. With multiple warehouses, complex variants, stock kept in an ERP or several marketplaces, a custom integration starts to make more sense.
Not sure which fits you? See our marketplace integration page or contact us and we’ll tell you what’s enough for your setup.